A study relating thiol:disulfide oxidoreduction to mechanism(s) of fluid transport and post-translational modification of protein structure is proposed. The site and mode of enhanced fluid transport across the corneal endothelium in vitro by such disulfide compounds that are physiological to the aqueous as glutathione disulfide and cystine is unknown. Methods to assess disulfide effects on the external cellular membrane will be based on the use of soluble polysaccharide derivatives of these disulfides (molecularly sized to obstruct cellular permeation) in conjunction with a specific membrane binding agent and thiol oxidizing and blocking agents. Physiological and/or biochemical parameters will be measured, respectively, during and subsequent to in vitro perfusion. Cellular interiorization by fluid-phase or adsorptive endocytosis will be assessed quantitatively by concentration, temperature and time-dependency of incorporation of a suitable marker. A reduction in the protein thiol:disulfide ratio that occurs during aging of the normal adult lens is markedly accelerated in senile cataract. Disulfide formation appears to be linked to the increase in water-insoluble protein and light scattering of the lens that accompany advancing cataract. Evidence that, in addition to mixed disulfides with glutathione, an appreciable amount of protein disulfides consist of protein-derived, low molecular weight thiols reassociated with the protein as mixed disulfides. Gel filtration, ion exchange and other chromatographic techniques will be used to separate and characterize these moieties.